The specific aims of this proposal are: 1) to test the hypothesis that prophylactic phenytoin (Dilantin) will lower the incidence of posttraumatic epilepsy in head-injured patients, and 2) to evaluate if that prophylactic phenytoin has any negative side effects on the neuropsychological-psychosocial recovery of head-injured patients. The study will be a longitudinal double blind design with patients randomly assigned to a treatment (phenytoin) or placebo group. Patients with pre-existing head injuries or CNS damage (including chronic alcoholism) will be excluded from this study. Patients will receive either a loading dose of phenytoin or placebo within the first 12 hours of head injury, and then subsequent daily dosages to maintain serum levels within therapeutic range. Study patients will receive treatment for a period of one year and then will be withdrawn from therapy (unless patients have had seizures occur). Both treated and control groups will be followed for a period of two years after injury to determine the incidence of posttraumatic epilepsy. Both groups will undergo extensive neuropsychological and psychosocial testing at one and 12 months (before drug discontinuance) to assess possible drug effects on these aspects of recovery. At the end of follow-up for all patients, the incidence of posttraumatic seizures will be evaluated for the treated and control groups and compared for statistically significant differences. Therefore, the objects of this proposal are to study prospectively the efficacy of prophylactic phenytoin in preventing post-traumatic seizures in head-injured patients and determine any effects this treatment might have on posttraumatic neuropsychologic recovery.